The present invention is directed to a hydraulic control system which includes a pair of control circuits individually fed by a pair of pumps and having a crossover network for automatically utilizing the fluid flow capability of the second pump for the first circuit under predetermined conditions.
Hydraulically operated material handling machines are well know which have two or more engine driven pumps for supplying pressurized fluid to the various motors and double acting hydraulic jacks thereof. These motors and jacks propel and maneuver the machine and also operate the material handling implements mounted thereon. The prior art in this area is exemplified by the following patents:
U.S. Pat. No. 2,445,781 issued July 27, 1948 to E. J. Hrdlicka, Jr.
U.S. Pat. No. 3,208,221 issued Sept. 28, 1965 to J. R. Schuetz
U.S. Pat. No. 3,693,350 issued Sept. 26, 1972 to J. D. Petro, et al
Brit. Pat. No. 1,044,851 published Oct. 5, 1966 to Auxitra, Societe Anonyme
Brit. Pat. No. 1,290,247 published Sept. 20, 1972 to Linde Aktiengesellschaft
Hydraulic control systems of the above-noted type frequently include a pair of pumps for individually supplying a pair of circuits having two or more motors. By selectively shifting the various distributor valves, fluid flow may be appropriately directed to the respectively connected motor for operation thereof. However, when these distributor valves and motors are disposed in interrupted series, sufficient flow is often not available to the downstream motor when the upstream motor is operated. Consequently, a separate manually operated control lever and associated hydraulic componentry is sometimes used to enable the flow from the second pump to be used to operate one of the downstream motors of the first circuit. The componentry to do this is often referred to as a crossover valve network and, in general, such network more effectively uses the available pump capacities. While a crossover network improves the multi-function capabilities of the system and effects economies of construction since fewer pumps and individualized control loops are required, it is sometimes undesirable to have to manually move another control lever to achieve the crossover function when the operator is busy manipulating the machine.
Still another problem is that while prior art control systems allow the fluid flow from two or more pumps to combine in order to operate a particular motor, and with the other motors usually being idle, such action often results in operating it too fast for conditions. Thus, full dual pump fluid flow is a deterrent to the controllability and efficiency of that motor and the related implement involved.